Generally, the conventionally-known multi-link, adjustable-stroke type engines which include: a plurality of links mechanically interconnecting a piston pin and a crank pin of a crankshaft; a control shaft having an eccentric cam provided thereon; a control link connected at one end to one of the plurality of links and connected at the other end to the eccentric cam; a reciprocating member connected at its distal end portion to the control link; a rotating member meshing with a proximal end portion of the reciprocating member via a screw section; a hydraulic pressure chamber facing the proximal axial end surface of the reciprocating member, and in which strokes of the piston are changeable by the rotating member being driven to rotate about the axis of the reciprocating member.
One example of such conventionally-known multi-link, adjustable-stroke type engines is disclosed in Japanese Patent Application Laid-Open Publication No. 2002-138867 (hereinafter referred to as “relevant patent literature”), which is constructed to pre-press the reciprocating member in the same direction as a load acting on the reciprocating member at the time of descending movement of the piston, so that a reciprocating load acting on the reciprocating member can be reliably prevented from undesirably inverting from a main direction (i.e., direction in which the load acts on the reciprocating member on the basis of a combustion or compression pressure applied to the piston) to an opposite direction.
In the commonly-known reciprocating type internal combustion engines, combustion pressure applied to the piston is transmitted to a single crankshaft via a con rod and output as rotational force from the single crankshaft; thus, normally, the piston combustion pressure acts on only one output shaft.
By contrast, the multi-link, adjustable-stroke type engine disclosed in relevant patent literature includes the plurality of links for controlling the position of the piston. Thus, in a case where a pivot point of one of the plurality of links is connected to an eccentric shaft, combustion pressure applied to the piston is transmitted, via the connected link, to both the crankshaft, which is an output shaft, and the eccentric shaft.
Further, in a case where the eccentric shaft and the crankshaft are interconnected via gears to synchronize rotations of the eccentric shaft and the crankshaft, rotational force caused by combustion pressure acting on the two shafts and by inertia force of motion parts would differ in a very complicated manner depending on an engine load and the number of rotations of the engine. Thus, driving/driven relationship between the gears would also change or switch several times per cycle.
Namely, by torque switching in response to which the driving/driven relationship between the gears switches, gear rattling noise is generated due to the backlash of the gears, so that engine noise would undesirably increase. As a means for suppressing such gear rattling noise caused by the torque switching, there has been known a “no-backlash gear” (scissor gear) mechanism in which two superposed gears are resiliently displaced from each other in their rotational direction via a spring so that the gear backlash can be eliminated. With the “no-backlash gear” mechanism, the spring load has to be great enough to appropriately endure torque inversion at the time of the torque switching; however, such a great spring load would unavoidably lead to increased friction sound etc.